We are studying the mechanisms regulating erythroid differentiation in cultured Friend Leukemia cells. We are concentrating on the characterization of different stability classes of messenger RNA in both uninduced and induced Friend cell cultures. We will use RNA synthesis inhibitors to terminate further RNA synthesis and at different times thereafter characterize the residual mRNA populations by both in vivo and in vitro experiments. The in vivo approach will involve 2 dimensional gel electrophoretic analysis of pulse labelled polypeptides. The in vitro studies will involve a characterization of the extracted mRNA using cDNA hybridization methodologies and in vitro protein synthesis.